How to activate ANOTHER object's actuator (Python)?
You do not do that. It is not supposed to "remote control" objects that way. 

You can indeed connect logic bricks of different objects. But this quickly ends in a chaotic mess. 

You can delete objects via endObject(). In difference to the actuator this does not need to be called by a controller of the object to be deleted.

Your sample could look like this:

import bge
scene = bge.logic.getCurrentScene()

for object in scene.objects:
    if object.name == "Critter":
        object.endObject()
        ...